At present, a Worldwide Interoperability for Microwave Access (WiMAX for short) standard is a broadband wireless access standard established by the Institute for Electrical and Electronic Engineers (hereinafter referred to as IEEE) Standard Organization, wherein a mobile WiMAX standard adds the support, such as terminal scanning and terminal handover mechanism in the mobile WiMAX standard, for the mobility of a terminal compared with a fixed WiMAX standard.
In the mobile WiMAX system, the terminal must perform scanning before it performs handover, so as to acquire the downlink signal quality, wherein the scanning can include intra frequency scanning and inter frequency scanning. With regard to the inter frequency scanning, the WiMAX protocol stipulates that the terminal can only achieve scanning consultation (negotiation) through the manner of the interaction of scanning request/scanning response (MOB-SCN-REQ/RSP) messages.
At present, the main triggering method of the scanning is a threshold triggering, and triggering (Trigger) parameters in a Downlink Channel Descriptor (DCD for short) of the mobile WiMAX standard defines the main triggering method of the scanning. Table 1 describes the triggering value (Trigger value) and average triggering period (average Trigger period) in the Trigger parameters, and Table 2 describes the type/function/operation in the Trigger parameters. As shown in Table 1 and Table 2, the triggering metric type (Trigger metric type) includes, but not limited to: Carrier to Interference Plus Noise Ratio (CINR for short), Received Signal Strength Indication (RSSI for short) and Round Trip Delay (RTD for short).
TABLE 1LengthNameType(1 byte)ValueType/54.11Refer to the description in Table 2Function/OperationTrigger 54.21This parameter is used for comparing Valuewith a measurement metric parameter so as to determine the trigger value of trigger conditionAverage 54.31Average trigger period is the period Triggerfrom averaging the metric measurement Periodvalues; when this average value reaches a measurement trigger threshold, the terminal responds with a specified trigger operation
TABLE 2NameLengthValueType2 bitsTrigger metric type:(MSB)0x0: CINR metrics0x1: RSSI metrics0x2: RTD metrics0x3: reservedFunction3 bitsThe calculation and definition of trigger conditions:0x0: reserved0x1: the metric value of neighboring BS is more than a certain absolute value0x2: the metric value of neighboring BS is less than a certain absolute value0x3: the metric value of neighboring BS is more than a relative value of the serving BS0x4: the metric value of neighboring BS is less than a relative value of the serving BS0x5: the metric value of the serving BS is more than an absolute value0x6: the metric value of the serving BS is less than an absolute value0x7: reservedNote 1: 0x1-0x4 cannot be used for an RTD metric methodNote 2: When Type 0x1 and Function 0x3 or 0x4 are used together, the scope of the thresholdvalue ranges from −32 dB (0x80) to +31.75 dB(0x7F); when Type 0x1 and Function 0x1, 0x2, 0x5 or 0x6 are used together, the threshold value is explained as an unsigned byte and its unit is0.25 dB, for example, 0x00 is expressed as −103.75 dBm, and 0xFF is expressed as −40 dBmOperation3 bitsOperations to be executed after a trigger (LSB)condition is met:0x0: reserved0x1: send scanning report (MOB_SCN-REP) message at every scanning interval0x2: initiate a handover request message (MOB_MSHO-REQ) of the terminal side0x3: terminal initiates the scanning process of neighboring Base Station or initiates theautomatic neighboring scanning (see 8.4.13.1.3), or triggers both of themsimultaneously through a scanning requestmessage (MOB-SCN-REQ).0x5-0x7: reservedNote: 0x3 is only used in the situation where the functions are 0x5-6
It can be seen from Table1 and Table 2 that according to the description in the WiMAX protocol, with regard to the metric method of the CINR, scanning can be triggered only through the absolute threshold triggering method of service base station downlink CINR measurement, i.e. when the CINR of the terminal under the serving base station is less or more than a certain CINR, the scanning will be triggered. However, because this method only considers the CINR at the source side, the CINR of a neighboring cell may be much more than the CINR of the current serving Base Station; nonetheless, since the CINR of the current serving Base Station does not reach the triggering threshold, the terminal will not perform scanning, and cannot hand over to the neighboring cell with a higher CINR, thus resulting in that throughput of the system cannot reach an optimum state.